Radio-communication transmitter



R. E. THOMPSON.

RADIO COMMUNICATION TRANSMITTER.

' .APPLICATION FILED SEPT.24,1917.

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INVENTOR.

R. E. THOMPSON.

RAD lO COMMUNICATION TRANSMITTER? APPLICATION FILED SEPT. 24, I917.

Patented June 7, 1921.

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i Specification of Letters Patent Application med September 24,1917. Serial no. 192,88

T0 allwhome'tmay concern: Y

Be it known'that 1, Roy E. T OMPSON, a citizen of't-he'United States, and a resident of New York city,-county of New York,

State of-jNewj'Y-ork, have invented certain new and :useful'lmprovements in Radioi Communication Transmitters, of which the efliciency of 1 electrical operation and followingis a specification. v

This'inventio'n relates to transmitting apparatus adapted for use'inradio telegraphy or telephony.

The object of the invention is to lncrease Sim- plicity ofmanipulativeuseIJ-j- The invent on consists of the novel rela-' tive arrangement and combination of ele-. ments which" is shown, by way of example, in the drawings, of which-' Figure 1 is a diagrammatic illustration of circuits and-apparatus in which the invenknown to-me and r I Fig. 2 isa" plan of the sparking arrangement R of Fig. 1; and

Fig. 3 is an end elevation of the same. The transmitter ofthis invention resembles, in outward appearance, transmitters of the type termed shock excitation or impact excitation or .quenched spark transmitters, but dillers therefrom in certain.im-

portant particulars, and said difi'erences produce eflicient energy-transfer and pure waveradiation under the novel condition ofab- -sence of any functional or critical relation of periods between the exciter circuit and the radiating circuit (antenna) and without any critical coupling between sald circuits,

functioning to aid in quenching the exciter,

as distinguishedfrom prior transmitters, in which either or both such functional or critical relations are essential to practical operation.

In Fig. 1 the radiating circuit (antenna) consists of aerial A, antenna tuning coil T, condenser K and earth connection 7E.

The frequency (and length) of the waves radiated is determined solely by the adjustment (arrow) of contact T on coil 1 (and sometimes by the adjustment of condenser K, when used, as preferred). Contact T is connected to aerial A by connection 103 through connection 102. A may be any properly constructed aerial structure. Although E indicates anearth or capacity connection, the entire antenna may be varied in corn struction.

The exciter circuit X; includes," coil I, condensers C, (Land which is shown'in detail'in Fig. 2. ()ne of the condensers C may be omitted and the entire lumped capacity-of the exciter made resident in-theother'condenserC. Sparking arrangementR needfrnotbe of the precise formr'shown or even of the fixed gap type shown, although this is the form and type which I have'found in practice to be best adapted to combination as an element of my transmitter.

' An. important feature of the invention is the relation between the exciter and the antenna in respect of the arrangement of coil 1'. *The exciter has one of its connections to t leads through antenna-portion 103 to adgustable or movable antenna-tuning contact one point of aerial A, such-as 102, so t at v T. The other'connection of the exciter is-to tion mayfbe; embodied in the best form Patented unem,

sparking arrangement R such point as to include coil I, such as point 7 10]. of the antenna other capacity E. The result of this arrangement is that for any adjustment of contact T there is just as much ofcoil I included in the exciter as in the antenna, and this arrangement maximum coupling. In other words, for any and all antenna periods obtained by moving contact T, or adjusting condenser K, or both, the coil 1 and its two circuit connections are common to the exciter and antenna. The object of the entire arrangement (which I believe to be the best form of various arrangements possible for accomplishing the same purpose) is to provide a maximum close coupling at all times. To

connection to earth or I of course produces the that end coil I is selected to have amply antenna of substantially all the energy set in flow in the exciterlupon the breaking down ofthe spark gaps same end, condenser K is preferably used on the shorter Wave-lengths, so that by its adjustment the antenna may be tuned without reducing the amount of coil 1 in common to both circuits. For diiierent powers and various antennae, no better directions to the constructor can be given than to provide a coil 1 of amply sufiicient inductance, the criterion of that being that the entire apparatus, with the other elements to be described, operates to cause efficient energy transfer from exciter to antenna, at all antenna wave lengths, irrespective oi approxi- R therein. To the.

mation of like periods in the two circuits, and with the same amount of coil I in both circuits so as to provide maximum coupling between them. Such operation may be determined by a comparison of the amounts of energy in the exciter and antenna respectively', and those amounts may be found in accordance with' any of the methods known to those skilled in the art.

A particular advantage of the special connection of coil I Shown, is that always when the period of the antenna is changed; to

energy which the charging condensers contain, we may consider the amount of power desired. This, of course, has a practical limit in the size of the antenna, and with my transmitter, it is inadvisable to employ more than 2 kw. with the ordinary ships antenna, on account of the chargi ng potentials and antenna insulation;

In view of the fact that there is produced 'a coupling which permits substantiallyinstantaneous; and complete transfer (111. e.,the operation described herein shows that this takes place during the first half-swing of current in the exclter), the charging or exciter condenserC has a value substantially of the order of the capacity of the antenna.

For use with, ordinaryships antennae, therefore, condensers C, C (or one alone) may have a total capacity of the order of .001 or .002 microfarad (mf.-). In order to obtain a'given power, a voltage is selected (for secondary S of transformerP, S sup plying theexciter as by way of sparking arrangement R, as-shown) which, with the selected value of capacity (3, will produce the required .power. Thus, for a '1 kw. transmitter I have found a supply voltage of approximately 25,000 to be most advantageous; and this voltage is varied for different powers, being, for example approximately 35,000 volts for a 2 kw. transmitter.

I usually emg vloy an alternator for the ultimate source at; and provide for transmitters of different powers a transformer P, S

adapted to give the required potential across the terminals of the e-xciter,; ,circuit X-: .(In

the power circuit the telegraph key Y or telephone transmitter may beconnected in any usual manner.)

In the unusual case where the antenna and antenna-capacity are large and out of proportion to the power of the restof the transmitting apparatus, it will be understood that my invention may be employed equally well, but that in such case the capacity of'thecharging condenser'may be substantially less than that of such an antenna. The above directions are for a large inductance and a small capacity in the exciter circuit, the ratio of capacity to inductance, therefore, being small, and the constructor should observe this carefully, for it is the reverse of the practice with so-calledquenched spark transmitters, which require for functional reasons alarge capacity and also a small inductance, thereby constituting a large ratio of capacity to inductance, and said small inductance resulting in a loose coupling. Also, whereas in my transmitter, the exciter-condenser is kept constant for all powers, with a given order of antenna-capacity, the ratio of capacity to inductance being kept small always, on the other hand, the quenched spark transmitters have increased the capacity of the exciter condenser for increase of power, so

that the large ratio of capacity to inductance.

for any given power was increased to a yet larger ratio for each increase of power. Also, in my transmitter the. charging potential is increased for increase of power, whereas in quenched spark transmitters the potential was kept constant for different owers. All thesedepartures'from standard prac- "tice have as their object such cooperation with the maximum coupling. permitted by the arrangement of coil 1, as will result in producing efficient and pure radiation without any critical conditions of tuning or coupling of the exciter and antenna circuits.

To the same end, the construction of the sparking arrangement R is such as to permit it to so function as to prevent the transfer back to the'exciter after the first half alternation orswing thereof, of the energy previously existing in the exciter during the first half swing,- which hasbe'en transformed to the antenna during that half swing. In my transmitter, as distinguished from quenched spark transmitters, there is no functional relation between exciter and antenna to form beatsof current which cooperate with the quenching spark-gaps to quench the sparks. In my transmitter the spark gap construction alone.must be relied on to cut off or open-circuit the exciter forthwith upon the instantaneous transfer ofits energy to the antenna. I provide fo'r'this increased duty of the sparking arrangement, chiefly by substantially increas ing the number of sparking electrodes, and also, preferably but not necessarily, by decreasing the sparking distance between them.

resistance can be set in operation in my trans' mitter on account of the high potentials I em ploy, which, as stated above, are as high as 25,000 volts for a 1 kw. transmitter. But on account of the provision of such a great number of cooling electrodes as 40 for a 1 kw.

transmitter, and the consequent distribution of the heat, this sparking arrangement has.

the ability of promptly open-circuiting the exciter as soon as its energy has been trans ferred to the antenna, so as to leave the antenna free to oscillate at its own natural period. In the quenched spark transmitter, the standard practice for all powers has had only about 16 spark gaps, of lengths usually 1n excess of a hundredth of an inch, and a charging voltage of 12,500 volts, these being,

used in an organization dependent on a critical coupling and critical tuning relation between the exciter and antenna whereby beats were produced which beats, with the lower supply-potential, aided the spark gaps in.

quenching the sparks after several swings of the exciter. The advantage of my transmitter is that the result, essential in practice, of efiicient transfer and of pure wave-radiation, is obtained without the troublesome operation of tuning or-coupling adjustments or both, relative to the exciter circuit X. Furthermore I believe and claim that this transmitter is the first in the art to actually operate in practice as a true impact excitation transmitter, z. 6., without any reaction by the antenna on the exciter, not even such a reaction as assists in quenching the exciter.

The particular sparking arrangement which I have employed, and which, arranged in'the combination as shown in Fig. 1, accomplishes the above results in connection with the specified circuit arrangement, is shown indetail in Figs. 2 and 3. As in the case ofthe several circuits and elements employed in this transmitter, so likewise in the case of this sparking arrangement, there is no broad novelty involved, so far as concerns the elements themselves or their general physical location in maximum coupling'for all diiferent periods of the antenna. The essentials, in order to permit this omission of clrcuittuning and critical coupling and yet obtain etficiency and pure wave-radiation, are as follows. In order to-obtain conditions which are coop erative with the above described extremely close coupling, the capacity of the excitercondenser is to approximate that of the antenna, and the ratio of capacity to inductance is to be small. There is to be an extremely large number of spark gaps, preferablywith minimum sparking distances; and

the charging potential is to be sufficiently high not onlyto breakdown the greatly increased number of spark-gaps but also to obtainthe desired power with the emittercondenser which is fixed for a wide range of power, and therefore the supply potential is to be varied for transmitters of different power. An exciter-condenser of different capacity is to be used .for an antenna of greatly different capacity.

In the form of sparking arrangement shown in Figs. 2 and 3' the details are designed so that it is practical and easy to operate the transmitter commercially with a sparking arrangement having gaps as shortas two or three thousandths of an inch, or even less, and that is the'object of the design of the specific sparking arrangement here disclosed; but I believe that various other designs and types of sparking arrangement may be employed in the invention, with the special arrangement of coupling and antenna-tuning, and the other. features of the invention, provided only that such sparking arrangements are so constructed or-arranged that they will open-circuit the exciter without any dependence on resonancerelation of the two circuits, and provided that the open-circuiting of the exciter is effected so promptly as to prevent the occurrence of coupling-waves and resulting impure radiation.

Referring to Figs 2 and- 3, R is an insulating base. There are two rows of gapelectrodes (marked at the bottom Fig. 2, numbers 2, 1, 7,8, 28, etc., to 9, and at'the top numbers 3,4, 6, 5, 16, etc). In Fig. 2, the base is broken away, to save space. Also, to avoid repetition of electrodes in the drawing, all of the multiplicity of gaps has beenomitted save a few at each end of the gap structure. The terminals of the circuit which includes the gap structure Fig. 1), are connected to electrodes 1 and 9 respectively.

The functioning gaps are between electrodes 1 and 2, 8 and 4, 5 and 6, 7 and 8, etc. Of these, the following are fixed to base R, z". 6., 1, 4, 5 and 8. The others, 2, 3, 6, 7, etc., are mounted on movable arms 10, which arms electrically connect electrodes 2 and -3 mounted on one arm 10, 6 and?- mounted on another arm 10, etc.

Of each pair of electrodes which include a spark gap between them (as 1 and 2), one '(asl) is fixed, and the other (as 2) 'is so mounted (nutatingly) on metallic arms 10,

which arms form part of the circuit. Arms 10 are mounted, by pins: 13 in slots 12, on strips 11 of insulating material.

\Vhen all of the functioning pairs of electrodes have been locked in parallelism, arms 10 are released from normal fixation to.

strips 11, so that said strips may be moved to the right (Fig. 2) so that the electrodes thereon, as 2 and 3, may come in contact with the members of their respective pairs, 7?. 6., electrodes 1 and 4; this being preparatory to the adjustment of all the gaps between the respective pairs by means of a single control to be described.

Thereupon arms 10 are again secured to strips 11, and said strips are moved to the left (Fig. 2) so that electrode 2 is slightly separated from electrode 1, and electrode'3 is likewise slightly separated from electrode 4; and sons toall the pairs of electrodes which areto have functioning gaps between them. This is effected b very accurate controlling mechanism, as ollows' The righthand ends of strips 11 (Fig. 2) are loosely held in a member 22, secured to base R, and

acting as a guide for said strips 11. The left-hand ends of the strips 11 are likewise held in a similar guide 21. The left-hand ends of strips 11 are connected together and provided with a threaded member 20 (Figs. 2 and 3), and by this the entire movable portion of the gap structure is shifted to the left"(Fig. 2) so as to cause the slight gap separation desired, as between fixed electrode 1 and movable electrode 2, between movable electrode 3 and fixed electrode 4-, etc.

Threaded member 20 passes throughja worm pinion 19, internally threaded in engagement with said threaded member 20. Pinion 19 has a ball-bearing support 23 in left-hand guide 21 (Fig. 2), so as to avoid friction between the rotating pinion 19 and its support which carries the movable portion of the gap structure, including the arms 10, which is the heavier part of the entire gap structure.

Pinion 19 has circumferential teeth, mesh ing with worm-drivel? (Fig. 3) mounted on left-hand guide 21 (Fig. 2) and operated by knurled head; 18 for adjustment of lengths of spark gaps. The proportions I employ are such that one complete turn of the knurled head 18 moves pinion .19 only;

Two elec-v are those (2,3, 6, 7 ,etc.) which are mounted on the conducting arms 10, which in turn are mounted on theinsulating strips 11.

The fixed. electrodes (as 1, 4, 5,3, etc.) i

are secured to base R by means of metallic members 15 and 14, which latter also serve as electrical connections between electrodes such as 4 and 5, which do not have a functioning gap between them.

It will be understood that a conducting arm 10 for two movable electrodes (as 2 and 3) is secured to strips 11 by one of the bolts 26 shown in Fig. 2; and that each fixed electrode (as 1, 4, 5, 8, etc.) and their connections as 15 (Fig. 2) are secured to the base R in the holes 24, 25 shown in base R in Fig. 2.

The circuit connections of the electrodes are from 1 to 9 as follows :-from electrode 1 across gap to electrode 2,-through arm 10 to electrode 3, across gap to electrode 4, through ecuring connection 15 to electrode 5, acrossgap to electrode 6, through supporting arm to electrode 7, across gap t o electrode 8, through connector 17 carrying screw 27 to an electrode not shown but secured to 17 by said screw 27 across gap to .electrode 28, through the next supporting arm 10 to electrode 16, and so on, down to the last electrode in circuit, ifL, electrode 9. That is, the leads from electrodes, 1 and 9* of Fig. 2 are connected in Fig. 1 as are the'single diagrammatic pair of gap elec-' trodes in Fig. 1'; and, as is shown by the above tracing of the circuit, the operating gaps are'between the following electrodes 1 and 2, 3 and 4, 5 and 6, 7and 8, etc.

, in operation, notwithstanding the lack of any tuning between the two circuits, and

notwithstanding their extremely close coupling, nevertheless pure wave radiation is obtained at all periods to which the antenna may be adjusted as I have proved by measurement with the Kolster decremeter. That is, for example, when the exciter has a period corresponding to a natural wave-length of 350 meters, I have found that pure radiation results when the antenna has any of the commercial wave-lengths, or even 800 meters or more. This fact of pure radiation with the accompanying high efficiency of energytransfer shows thatthe exciter m is open-circuited very quickly after the breaking down.

of the spark gap.

The over-all eficiency of this tran mitter has been measured, 5. 6., the ratio of the energy supplied to the exciter X, to the amount of energy radiated as wavesyand this efficiency has been found to be frbm 60 to 75 per cent. This fact shows that substantially all. (or a very large part indeed) of the supplied energy is transferred from exciter to radiator in'the extremely brief interval of time between the occurrence of the spark discharge and'the time of open-circuitin of exciter X. I

in View of the fact that pure radiation is accomplished with suchan extremely close coupling as that by coil I, and with suchgreat efficiency, it is clear that exciter X is open-circuited at the end of its first half oscillation, i. 6., the first time the current falls substantially to zero after the break-' ing down of the spark gap.

Such a result has never been accomplished by any other transmitter. In this transmitter, the means for energy-transfer and the type of sparking arrangement are such that,

when the two circuits have as substantially diflerent eriods as 300 for the exciter, and

1050 for t e antenna, the exciter is open-circuited sufiiciently promptly after the spark discharge to permit the above stated high ethciency and economy of energy-transfer and to prevent radiation of waves of a frequency different from the period of the antenna.

I claim:

In a radio transmitting apparatus, a combination with an exciting circuit of non-persistent oscillatory character. of a radiating circuit of a persistently oscillating character; and means for coupling said circuits and having a coupling value sufficient to cause the transfer of energy from the exciting circult to the radiating circuit when said clrcuits are not tuned to the same period; and a multiplicity of spark gaps equally adjustable from a single control in the exciting circuit for preventing the transfer of energy from the radiating circuit to the exciting circuit while permitting transfer of energy from the exciting circuit to the radiating circuit, substantially as described.

ROY E. THOMPSON. 

